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ACS Biochemistry Exam– Questions & Complete Solutions
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ACS Biochemistry Exam– Questions & Complete Solutions
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ACS Biochemistry Exam– Questions & CompleteSolutions
Metabolism (catabolism and anabolism) Right Ans - Metabolism: sum of
total chemical reactions in an organism, also the method by which cells extract
and use energy from their environment.
Catabolism: The process by which stored nutrients and ingested foods are
converted to a usable form of energy. It produces simple products CO2, H2O,
NH3, and building blocks such as sugars and fats that are used in anabolism.
Anabolism: the process by which simple products and building blocks of
catabolism are used to create complex biological products that contribute to
organismal growth and development. It also uses the energy produced in
catabolism to do biological work.
Properties of cells Right Ans - Metabolism: undergoing catabolic and
anabolic processes.
Reproduction: cell populations grow via asexual reproduction.
Mutation: during growth and reproduction, cells sometimes make mistakes,
leading to mutations and evolution.
Respond to environment: metabolic pathways respond to signals, including
light, touch, hormones, and nutrients, that can turn the pathways on or off.
Speed and efficiency: cell operations are highly specific to maximize targeting
and efficiency.
Similar building blocks: most species are very similar at the cellular level.
What accounts for water's unique properties? Right Ans - Hydrogen
bonding
The unique properties of water (specific heat, heat of vaporization, solubility)
Right Ans - 1) high specific heat, or heat required to raise the temperature of
the unit mass of a given substance by one degree.
,For water to increase in temperature, water molecules must be made to move
faster, or get higher KE, and doing this requires breaking hydrogen bonds,
which absorbs heat. So, as heat is applied, most of it goes to breaking the
bonds not upregulating KE, thus making water harder to heat than substances
where no bonds need to be broken.
2) High heat of vaporization, or the amount of heat needed to turn one g of a
liquid into vapor, without a temperature rise in the liquid. Important for sweat
because it ensures that when the liquid evaporates from our skin, the heat
required for the transition is kept in the gas, causing a net cooling effect on the
skin.
3) Unique solubility properties: "like dissolves like". Water dissolves polar
molecules and ions, and can act as an H-bond donor or receptor
4) Amphoteric, it can act as an acid (donating electrons) or a base (accepting
electrons). The conjugate acid of water is the hydronium ion, H3O+, and the
conjugate base of water is the hydroxide ion, OH-.
Keq for water at 25 degrees C and in pure water Right Ans - At 25 degrees
C:
Keq= Kw= [OH-][H3O+]= 1*10^-14
In pure water:
[OH-]=[H3O+]= 1*10^-7
Calculation for pH and pKa Right Ans - pH= -log[H3O+]
pKa= -log(Ka)
Normal blood pH range Right Ans - 7.35-7.45
The Hydrophobic Effect Right Ans - When non-polar molecules aggregate
in the presence of water, minimizing the entropy decrease water must go
through to order themselves around the border of the non-polar molecule.
Reducing the surface area water must organize around increases entropy,
which is favorable.
The aggregation is responsible for the formation of a variety of lipid
structures in the body, including cell membranes.
,Buffers Right Ans - Composed of a weak acid (HA) and its conjugate base
(A-). Added acid reacts with A-, and added base reacts with HA, giving a
limited overall pH change.
Two main reactions:
1) When excess base is added:
OH-+HA-->H2O+A-
2) When excess acid is added:
H+ + A- -->HA
**So, the net result is more of the weak acid and its conjugate base**
When are buffers optimal? What equation can we use for this? Right Ans -
When [HA]= [A-], occurring when pH=pKa
Henderson- Hasselbalch allows use to calculate pH at given pKa, and vice
versa:
Blood Buffering Right Ans - Components:
1) carbonic acid (H2CO3) (weak acid). pKa= 6.1.
2) Bicarbonate Ion (HCO3-), conjugate base of carbonic acid
3) H+ (hydrogen ion)
If OH- (base) is added, Carbonic acid buffers it into bicarbonate ion and water.
If H+ (acid) is added, bicarbonate ions and H+ buffer it to carbonic acid.
Amino Acids, peptides, and polypeptides Right Ans - the building blocks of
proteins, a chain of which is called a peptide. There are 20 standard amino
acids that act as the monomers to make protein polymers!
A long peptide is called a polypeptide!
Proteins are composed of one or more polypeptide chain.
Peptide bonds Right Ans - Between the C and N of C=O and N-H of two
adjacent amino acids.
, What wavelength is indicative of aromatic amino acids? Right Ans - 280
nm, with tryptophan absorbing more, tyrosine absorbing a bit less, and
phenylalanine absorbing a lot less.
Stereochemistry of amino acids Right Ans - Every carbon except for glycine
is a chiral center, giving two possible structures for each: L and D (except for
glycine).
L is the only one found in nature.
Acid-Base properties of amino acids Right Ans - Each has at least two
ionizable protons (from the COOH and NH3 groups), but most have others.
COOH pKa: 2.34
NH3 pKa: 29.60
PI Right Ans - the isoelectric point, or the pH at which an amino acid or
peptide has no net charge.
- At pH= PI, the predominant species is the zwitterion
- At pH<PI, the predominant species is net positive
- At pH>PI, the predominant species is net negative
**At PI, amino acid or peptide cannot migrate through an electric field, so this
is a way we can separate amino acids (by PI via electric field!)**
How to calculate PI, or isoelectric pint Right Ans - Average pKa values
involving the neutral species
For glycine, that only has COOH and NH3 pKa's, the PI is the average between
2.34 and 9.60, so 5.97!
Essential Amino Acids Right Ans - Those that cannot be made in the body
and thus must be obtained via the diet. Some can be made from others, so it
isn't a hard line, but:
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